Stanford Today
Edition: November/December, 1996
Section: On Campus
WWW: Scientific Serendipity

Research on lasers led chemists into Mars project

By Janet Basu and David F. Salisbury

Zare and generations of graduate students have devised ways to use lasers to detect substances stuck to the surface of objects, in amounts so small that ordinary chemical analysis would destroy or contaminate the substances. As part of that work, the researchers built a "two-step laser mass spectrometer" that is the most sensitive instrument of its kind in the world.

That sensitivity attracted NASA scientist David McKay and his colleagues at the Johnson Space Center in Houston. Two-and-a-half years ago, they sent several slivers of a mystery rock to Zare's lab, with this request: Analyze the rock, but handle it very carefully. Later, they explained why. The precious slivers were cut from deep inside a meteorite. Recent studies had shown that it almost certainly was formed on the planet Mars, then tossed into space during a giant asteroid impact and dropped on Antarctica some 13,000 years ago.

In the center of the meteorite, McKay's team had found tiny egg-shaped and tubular structures that looked like fossils of minuscule bacteria. Evidence from Zare's lab provided critical support for the idea that those structures really might once have been alive.

Zare found a unique combination of everyday air pollutants called polycyclic aromatic hydrocarbons (PAHs) that form when living things die. Because the PAHs were concentrated in the center of the meteorite, they did not appear to be contaminants picked up on Earth. The concentrations peaked near the possible microfossils.

At first, says former grad student Simon Clemett, who worked on the project with Claude Maechling and Xavier Chillier, no one dared breathe the "L" word. Eventually, though, every test they could devise pointed to the same conclusion: Several lines of evidence can be explained most simply by the hypothesis that primitive life existed on Mars about 3.6 billion years ago.

Now that the public clamor has quieted down, the scientists involved still must test the Martian life hypothesis. Zare's lab is looking for traces of amino acids, the building blocks of life. Many other researchers are designing experiments, including some that may ship on spacecraft aimed at Mars.

As intriguing as the Mars findings are, no one is promising solid proof soon. As Zare says, "It is very difficult to prove that life existed 3.6 billion years ago on Earth, let alone on Mars." ST